1. Field of the Invention
The present invention relates to a process for conducting multiphase reactions, especially the preparation of xcex1,xcex2-unsaturated ketones by condensation of aldehydes with ketones.
2. Discussion of the Background
xcex1,xcex2-Unsaturated ketones are very reactive and hence used in a multiplicity of organic syntheses. For example, they are intermediates for the preparation of scents and pharmaceuticals.
It is known from Houben-Weyl, Methoden der organischen Chemie, Volume 7/1, pages 77 ff, and Organic Reactions, Volume 16, pages 27-47, 69-78, 177 ff, that aldehydes can be reacted with ketones to form xcex1,xcex2-unsaturated ketones. Temperatures of 5 to 25xc2x0 C. are preferred for these condensations (Organic Reactions, loc. cit., page 77). The numerous catalysts employed in these processes, for example alkali and alkaline earth metal hydroxides, organic bases, alkali metal salts, alkoxides, also catalyze the self-condensation of the aldehydes or ketones and therefore lead to by-products as well. The workup of such mixtures is costly and inconvenient, since the catalyst used has to be removed again or neutralized. Target product yields are frequently unsatisfactory.
DE 2150992 describes a process for preparing xcex1,xcex2-unsaturated ketones from formaldehydes and ketones. The aldol condensation is catalyzed by a catalyst consisting essentially of zinc oxide. The reaction is carried out at temperatures of 140xc2x0 C. to 200xc2x0 C. The ketone is used in excess. The reaction mixture is worked up by distillation. Molar ratios in the range from 1.3/1 to 5.7/1 between the ketone and aldehyde provide conversions of 66% to 82%, based on the aldehyde used in deficiency, while xcex1,xcex2-unsaturated ketones are obtained in selectivities of 75% to 93%, depending on the identity of the materials used. Since the reaction mixtures contain only 20% to 60% of the target product, the separation cost and inconvenience is considerable.
EP 0792 862 A1 discloses a process for reacting aldehydes with ketones over a complex magnesium aluminum hydroxide. The aldehyde, which is used in deficiency, combines with the ketone used to form not only the aldol addition but also the aldol condensation product in a molar ratio in the range from 0.7/1 to 1.40/1. These two products are formed together in a selectivity, based on aldehyde, of only 71% to 79% at an aldehyde conversion of 96% to 98%.
U.S. Pat. No. 5,583,263 describes a two stage process for producing xcex1,xcex2-unsaturated ketones, especially the reaction of n-butyraldehyde with acetone. The first stage comprises reacting the reactant mixture, which contains acetone in excess, over a basic ion exchange resin to form xcex2 hydroxy ketones. n-Butyraldehyde is converted into 4-hydroxyheptanone in a selectivity of up to 88% at complete conversion. At the same time, diacetone alcohol is by-produced from acetone in a selectivity of up 95%. The crude mixture of the first stage is dehydrated in the second stage under acid catalysis to form the xcex1,xcex2-unsaturated ketones. The catalysts used are strong acids or a strongly acidic ion exchange resin. The yield of hept-3-en-2-one, the condensation product of n-butyraldehyde and acetone, is 85%, based on n-butyraldehyde. The diacetone is converted into mesityl oxide. This process is accordingly a process for coproducing two xcex1,xcex2-unsaturated ketones. The use of this process is disadvantageous when only one aldol condensation product, especially that of aldehyde and ketone, is the target product.
WO 91/07368 discloses a further two stage process for preparing xcex1,xcex2-unsaturated ketones from aldehydes and acetone. The first stage comprises reacting the aldehyde with acetone, used in excess, under catalysis by cyclic amines (perhydroisoindole and pyrrolidine derivatives) in the presence of water to form the corresponding xcex2-hydroxyketone. After aldol addition has taken place, aqueous mineral acid (sulfuric acid, hydrochloric acid) is used to set a pH of 4.5 and a mixture of acetone and water is distilled off. The crude mixture is converted to the target product by elimination of water by admixing the crude mixture with a mixture of hydrochloric acid and chloroform and refluxing it. The target product is isolated by phase separation, washing and distillation. The yields of xcex1,xcex2-unsaturated methyl ketones, based on aldehyde used, are between 80% and 90%. Disadvantages of this process are especially the high workup cost and inconvenience and the use and consumption of auxiliary materials.
EP 0 816 321 A1 discloses preparing xcex1,xcex2-unsaturated methyl ketones by crossed aldol condensation of aldehydes with acetone in a batch operation. The catalyst used is 2% aqueous sodium hydroxide solution, and acetone is used in excess. The reaction takes place in the temperature range 70-72xc2x0 C., and the reaction time is about 4.5 h. When isovaleraldehyde is reacted with acetone, for example, 6-methyl-3-hept-2-one and 6-methyl-4-hydroxyheptan-2-one are obtained in 66% and 3.3% yield respectively, based on isovaleraldehyde, the conversion of which is 98.3%. The process has the disadvantages that it is a batch process and that the yield of target product is unsatisfactory.
The abovementioned processes are unconvincing with regard to cost convenience and/or space-time yields.
It is an object of the present invention to develop a more economical process.
The processes mentioned above involve at least one multiphase reaction (solid-liquid or liquid-liquid). The inventors have improved the multiphase reaction, especially that between substantially immiscible liquids.